Do these people who are giving you a hard time know that this is happening in the context of Mono pursuing his new relationship in a way that most poly people (or so it seems to me from my reading here, at least) wouldn't find ethically acceptable? I mean, it seems like that must be having an impact on your ability to be cool with things. You dont have the option to meet her, come to trust her, the stuff that normally a poly person suffering new-metamour-jitters could do to reassure themselves.
Me, 30ish bi female, been doing solo poly for roughly 5 years. Gia, Clay, and Pike, my partners. Davis, ex/friend/"it's complicated." Eric, Gia's husband. Bee, Gia and Eric's toddler.